Manufacture of acetic anhydride and acetaldehyde from ethylidene diacetate



Patented Mar. 30, 1926.

UNITEDSTATES MELVILLE .1. mmsmr. AND on'oncn s. smw, or snawmrom FALLS, comme- 1,578,454 PATENT OFFICE.

CANADA, ASSIGNOBS, BY HEBNE ASSIGNMENTS, TO CANADIAN ELECTRQ yBoD c g COMPANY, LIMITED, 0! MONTREALGANADA.

mnrncrunn or AOETIC mnynmnn AND aonrannnmrnn raou' n'rmmnnn nncnm'rnp Io Drawing.

To all whom it may concern:

Be it known that we, MELVILLD J, MAR- SHALL and Gnoaon S. SHAW, both sub'ects of the King of Great Britain, and resi ents of the town of Shawinigan Falls, in the Province of Quebec and Dominion of Canada, have invented certain new and useful Im rovements in the Manufacture of Acetic Anliydride and Acetaldehyde from Ethylidene Diacetate, of which the following is a full, clear, and exact descri tion.

This invention relates to improvements in the manufacture of aceticanhydride and acetaldehyde from ethylidene diacetate, and the object of the invention is to provide for an increased reduction of anhydride.

A further 0 ject is to avoid the formation of tar and the consequent production of acetic acid.

In the production of acetic anhydride from ethylidene diacetate according to the equation;

cmcmooccmu-acmcoaoq-cmcno as the disadvantage that there is consider-' able secondary reaction producing a large amount of acetic acid relatively to the anhydride.

According to this invention, the formation of anhydride is increased and the formation of acetic acid decreased as compared with previously known results, by heating the ethylidene diacetate to ebullition and adding thereto at suitable intervals a small amount of phosphoric acid to serve as a catalyst. The catalyst should be added only in very small amounts, since if an excess of catalyst is present tar formation and the production of largely increased amounts of acetic acid are unavoidable. The catalyst should therefore be added only in amounts and at intervals 'suflicient to maintain the reaction at reasonable velocity.

Application Med January as, 1920. Serial in. 354,225.

A comparison of the results obtained according to this invention with results obtamed by the use of other catalysts is shown 1n the following table lnfi d rl d Catalyst to La:

- acid 7 produced Ammonium rsul hate sulphuric wh D I di Phosphoric aci 9. 1

a time, at intervals of 15 minutes to 30' minutes, till 4 gms. in all have been added. It is found that this rate is sufficient to keep the aldehyde coming off at a fairly constant rate. I

This aldehyde on being condensed amounts toabout 250 gms. with a content of about 5% acetic acid, which can be separated from the aldehyde by fractional distillation. In most cases, however, the acetic acid passing over with the aldehyde is'quite small in amount.

' Starting with nearly pure ethylidene diacetate 740 gms. of a liquid of the following composition is eventually left in the decomposition vessel:

Per cent. Acetic anhydride 75. 0 Acetic acid 8. 0 Ethylidene diacetate 17. 0

Thus fully 87.4% of the total ethylidene diacetate present has been decomposed.

This acetic acid and anhydride arethen distilled from the vessel through a rectifying column and condensed, till onl ethylidene diacetate remains behind, or t e undecomposed ethylidene diacetate may be purianhydride containin'g some ethylidene diactate, is subjected to a further fractional distillation in a second still fitted with a very eflicient rectifying column. In this way, a mixture of acetic acid and acetic anhydride is obtained practically free from ethylidene diacetate.

This mixture normally conta1ns- 80%- to 90% acetic anhydride, which is better than the ordinary commercial material. For this reason it is not necessary to separate any of the acetic acid from the 'anhydride by fractional distillation.

While it has been stated in the foregoing example that concentrated phosphoric acid a is used and the process carried on at atmospheric pressure, it will be understood that these conditions pertain solely to the particular example given and that the invention is not limited thereto, as the process may be carried on under any pressure practicable either sub-atmospheric or super-atmospheric and with dilute acid.

While for all practical purposes, the addition of phosphoric acid up to 1.5% of the weight of the diacetate will be sufiicient, it may nevertheless be found advisable imder certain circumstances to add further acid, and therefore this invention contemplates the addition of acid up to approximately 5.0% of the weight of the diacetate. While the superior results of this process are due largely to the use of phosphoric acid,

they are also due partly to the manner in which the acid is introduced.

In the foregoing specification, certain amounts of acid have been referred to and it 'will be understood that these amounts are free acid or acid available for the reaction of the invention. If the rocess is carried out in a vessel of iron, a uminum, copper or any other ordinary metal, the metal is slowly dissolved and precipitates a portion of the phosphoric acid as an i nsoluble phosphate. Therefore when apparatus is used which is attacked by the acid,

it will be nece:sary to add an excess of acid over the requirements of the process. Apparatus of-glass or earthenware is not destroyed, but is not satisfactory from a commercial point of view and the process will therefore preferably be carried out in metal apparatus protected by suitable enamel.

The ethylidene diacetate as found in com-' In carryin'gout the process, although the material may be at the temperature of the boiling point of ethylidene diacetate at the commencement of the process, the tempera ture of the li uid may drop very materially after the addition of the\catalyst, and may remain at a temperature below'the boiling point of ethylidene diacetate, although the 1 material still has the appearance of boiling.

This appearance of ebullition is due to the escape of a mixture, chiefly of acetaldehyde and acetic anhydride, which, under the conditions of the reaction, come offat a temin ebullition and the produced acetaldehyde A continuously distilled off through a rectifyingcolumn, the temperature of which is adjusted to permit the passing off of aldehyde only.

3. A process for the manufacture of acetic anhydride and acetaldehyde from ethylidene diacetate, which includes adding phosphoric acid to the ethylidene diacetate at intervals of time until most of the diacetate'is decomposed and maintaining a temperature sufficient to keep the reaction liquor in ebullition.

4. A process according to claim 3, in which the proportion of each addition of catalyst to the diacetate is approximately 03% by weight. V

5. A process for the manufacture of acetic anhydride and acetaldehyde from ethylidene diacetate, in which the diacetateis heated to ebullition with up to 5.0% of its weight of phosphoric acid added in small amounts to ebullition with up to 1.0% of its weight of phosphoric acid for the duration of active decomposition, and. the heating continued with additions of phosphoric acid until most of the diacetate has been decomposed.

7. A process for the manufacture of acetic anhydride and acetaldehyde from ethlidene diacetate, in which the diacetate is heated to ebullition with phosphoric acid under .a rectifying i column and acetaldehyde recovered at the outlet of the column during the decomposition of the diacetate, the residual liquor being subsequently distilled off until only ethylidene diacetate remains,

and the distillate freed from entrained dride and ucetaldehyde, which con'iprises total amount of acid added being not more adding phosphoric acid to ethylidenc diacethan 5% of the weight of ethylidene diace- 10 tate, heating the mixture and continuously -tate. separating the produced acctaldchyde. 111 witne s whereof, we have hc-l' eunto set 9. A method of producing acetic anhyour hands. dride and acetaldchyde,- which includes the step of gradually adding phosphoric acid MELVILLE J. MARSHALL. t0 ethylidene diacetate while heating, the GEORGE S. SHAV. 

